Award: PLR-1142174

Marine food webs are structured by top-down (predation) and bottom-up (production) forces, but rarely can the effects of predation in open-water systems be assessed. This project used an acoustically equipped autonomous glider in the southern Ross Sea, Antarctica, to assess changes in the distribution of penguin prey (crystal krill, shrimp-like organisms, and silverfish, small fish that are energy rich food items) and the oceanic environment (temperature, salinity, oxygen, single-celled plankton concentrations that are the food of krill), along with satellite linked time-depth recorders on Adélie penguins and censuses of co-foraging whales to assess predation pressure and changes in availability of krill and silverfish. The glider was deployed from late November from the fast ice near McMurdo Station and recovered by a research vessel in early February; it collected data continuously during this entire period. Prey depth and abundance were uncoupled from their plankton food, but were strongly altered by changes in predation pressure. Penguin foraging increased in distance and duration as more penguins and whales entered the area. Penguins in turn modified the vertical distribution of their prey (krill and silverfish), as the mean depth of krill increased from 45 to 65 m through time. Silverfish also went deeper, but their maximum change only from 52 to 57 m. Penguins fed more on fish as the season progressed (and depth of krill increased). The project measured changes in oceanic conditions and plankton over short time scales and was one of the first projects to ever use these new technologies in a restricted environment. The project demonstrated that both top-down and bottom-up processes are important to the food web of the Ross Sea, and also demonstrated the power of using new technologies in remote and difficult environments. Last Modified: 09/14/2015 Submitted by: Walker O Smith